1. Field of the Invention
The present invention relates generally to piezoelectric devices, and more particularly to piezoelectric electro-acoustic transducers for use in piezoelectric sounders, piezoelectric telephone receivers and other devices. The invention also relates to a piezoelectric electro-acoustic transducer having an improved terminal for interconnection with a piezoelectric diaphragm.
2. Description of the Prior Art
Conventionally, various types of electro-acoustic transducers utilizing the piezoelectric effect are known. For example, Published Unexamined Japanese Patent Application (PUJPA) No. 5-111085 discloses a ceramic receiver which includes a piezoelectric diaphragm that consists of a lamination of a metal plate and a piezoelectric element on the surface thereof and that is contained inside a casing, wherein a metal terminal is connected at one end thereof to the piezoelectric diaphragm plate and the other end of the metal terminal extends to outside of the casing. Interconnection of the metal terminals to the piezoelectric diaphragm is done by soldering or spring-contact techniques.
A piezoelectric telephone receiver is disclosed in PUJPA No. 7-203590, wherein a piezoelectric diaphragm consists of a metal plate and a piezoelectric ceramic plate laminated on one surface thereof, and is contained inside a casing while associated lead wires are coupled to the piezoelectric diaphragm such that the lead wires extend to outside of the casing.
As disclosed in PUJPA Nos. 5-111085 and 7-203590, the prior art piezoelectric electro-acoustic transducers have been structured such that the piezoelectric diaphragm is supported inside the casing while the piezoelectric diaphragm is connected to one end of a lead wire or a metal terminal with the lead wire or metal terminal being elongated to extend outside of the casing.
Incidentally, in the recent years, overall size and thickness reduction are becoming important more and more in the manufacture of various types of products. This is also the major trend of electronic parts or components which are to be assembled or provided in various electronic products. Accordingly, overall size and thickness reduction are also highly demanded for the manufacture of piezoelectric electro-acoustic transducers.
However, in piezoelectric electro-acoustic transducers having the structure for storing and holding the piezoelectric diaphragm within the casing, where an attempt is made to accomplish size and thickness reduction, a required gap space will likewise decrease in size between the piezoelectric diaphragm and associated surrounding portions of the casing. This can adversely increase the risk of having an electrode takeout structure, consisting of lead wires and/or metal terminals, contact the inner wall of the casing, which prevents effective vibrations of the piezoelectric diaphragm. As a result of such contact, the sound pressure is decreased, and the resonance frequency increases beyond a desired resonance frequency, thereby rendering it impossible to obtain any desired transducer characteristics.